Details

Introduced backup node which maintains the up-to-date state of the namespace by receiving edits from the namenode, and checkpoint node, which creates checkpoints of the name space. These facilities replace the secondary namenode.

Description

Currently Secondary name-node acts as mere checkpointer.
Secondary name-node should be transformed into a standby name-node (SNN).
The long term goal is to make it a warm standby.
The purpose of this issue is to provide real time streaming of edits to SNN so that it contained the up-to-date namespace state.